The present invention relates to an ink jet print head provided in an ink jet type recording device, and more particularly, to a method for improving the reliability and accuracy of ink droplet ejection from an ink jet print head by regulating the drive signals that effect ink droplet ejection.
Some conventional ink ejection devices employ a piezoelectric ceramic element to alter the capacity of an ink chamber containing ink. An ink droplet is expressed from the ink chamber through an associated nozzle when the capacity of the ink chamber is decreased, and ink is introduced into the ink chamber through an ink inlet when the capacity of the ink chamber is increased. This type of ink jet print head is formed with a plurality of ink chambers. The ink chambers are separated by partitions formed of a piezoelectric ceramic material. An ink supply device, such as an ink cartridge, is connected in fluid communication on one end of the plurality of ink chambers, while ink ejection nozzles (hereinafter abbreviated to nozzles) are provided on the other end of the plurality of ink chambers. When drive signals are applied to the partition walls, the partition walls are deformed. This deformation decreases the capacity of the interposed ink chamber and generates a pressure wave in the ink that forces an ink droplet to be ejected through the associated nozzle onto a recording medium, forming characters, patterns, and the like.
If variations exist in the dimensions of the ink chambers or nozzles, however, the ink droplets cannot be reliably ejected from the nozzles in an accurate direction, even when the ink jet print head is driven by a regulated drive waveform. This is evident when unevenness appears in dot arrays recorded on the recording medium and when the recording device cannot achieve a prescribed recording quality.
The consistency of this ink droplet ejection is dependent on both the time required for the pressure wave generated in the ink to propagate once across the length of the ink chamber and the pressure wave generated by the drive waveform. These two factors cannot be coordinated if variation exists in the dimensions of the ink chambers. As a result, the ink droplets cannot be reliably ejected with an accurate aim. Due to this problem, it is necessary to require extremely strict tolerances for the dimensions of the ink chambers and nozzles during the production process in order to maintain a uniform printing quality for each ink jet print head.
According to the method proposed in Japanese Laid-Open Patent Application (Kokai) No. HEI-7-32651, a plurality of test images is recorded on a recording medium, and the density of these test images is measured using an optical scanner. Next, a characteristic curve is graphed using the measured density and drive control values. The characteristics of each ink jet print head are optimized by calculating the optimal value of the derived control values for each ink jet print head based on the characteristic curvature, test results, test control values, and desired density. However, this method of calculating the optimal drive control value is not efficient because it requires a large number of processes. In addition, the above process does not consider the consistency of the ink droplet ejection direction, which has a major effect on the recording quality. Accordingly, this process is not sufficient for reliably achieving and maintaining a prescribed printing quality.